Polyamide resins of the aforementioned type have long been known. For instance, Ullmann's Encyklopadie der technischen Chemie, 3rd Ed. (Munchen-Berlin: Urban & Schwarzenberg Verlag, 1963) in Vol. 14, pp. 73-75 describes polyamide resins which are prepared from amines such as ethylene diamine and other polyethylene amines and branched dicarboxylic acids made from unsaturated fatty acids. The use of trimeric fatty acids and monomeric or trimeric carboxylic acids for the composition of such polyamide resins is also mentioned.
Mentioned as fields of application for these polyamides, which are of a waxy or resinous character, are, among other applications, the curing of epoxide resins, the bonding of raw materials, the manufacture of composite component parts, and the like.
Polyamide resins find a further field of application as adhesion promoters, especially in so-called plastisols. These are liquid to pasty dispersions of a powdery polymerisate in a plasticiser.
Plastisols are used, for example, for heat- and sound-insulating layers, for protection against corrosion and stoning (damage caused to coated bodies by stones or pebbles impacting on their surface), which in this case are principally applied in the construction of automobiles by means of application onto various kinds of metal surfaces. While plastisols can display certain adhesive properties, these do not always comply with the today's high requirements. For there is insufficient adhesion in certain places after application of the protective layer or if the adhesion loosens in due course, corrosion may set in very rapidly. Also in the case of mechanical stress the protective layer may come off.
So far, there has been no lack of attempts to improve the various polyamide resins in order to adapt them for certain applications. The objective of this development work has been the improvement of polyamide resins for their use as adhesion improvers or adhesion promoters, with regard to their adhesive properties, processability, intake of water, storage stability, and their resistance to high temperatures, light, and radiation.
This has already been attempted and accordingly, German Patent Specification 3 111 815 describes the improvement of the adhesive properties of plastisols by condensing 0 to 0.5 equivalents of certain polycarboxylic acids originating from the polymerisation of unsaturated fatty acids and 0.5 to 1 equivalents of dicarboxylic acids such as adipic acid with 1 to 2 equivalents of particular aliphatic polyamines. However, the thermal stability of these plastisols still leaves something to be desired.